1. Technical Field
Embodiments of the disclosure are directed to an intelligent hardware and software system, possibly embedded and/or distributed, that monitors parameters and events related to changes in the thermal stratification of a water body.
2. Discussion of the Related Art
Thermal stratification occurs in water bodies, both freshwater and marine bodies, as a result of density variations in water as a function of temperature and other variables. The stratification process may be seasonal and can depend on a number of factors including geometry, geography (i.e., latitude, etc.), weather and climate, flows, turbulence, and currents.
Stratification results in three layers of water: (1) an upper (generally) well mixed layer, known as the epilimnion; (2) a transitional zone characterized by rapidly changing temperature, known as the metalimnion; and (3) a dense lower layer, known as the hypolimnion. A thin layer exists within the metalimnion having the greatest water temperature change is known as the thermocline.
Underwater acoustics are affected by stratification, as the velocity of sound changes with temperature, as well as salinity and hydrostatic pressure. In fact, the thermocline can act as a barrier or even a waveguide of sorts for sound. In the marine environment, it is important to understand this phenomenon because it affects underwater communications and military applications such as passive and active SONAR employed for antisubmarine warfare (ASW).
In the case of freshwater lakes, stratification has implications for water quality in that the metalimnion acts as a barrier for oxygen exchange with the mixed upper layer. Reductions in dissolved oxygen can affect patterns of fish behavior as well as change the water chemistry in that nutrients such as nitrogen and phosphorous become more soluble under anoxic conditions and can be released from bottom sediments. These nutrients, which can also affect fish, may later mix with the upper layer and stimulate algal blooms. Algal blooms can further reduce dissolved oxygen levels and also introduce toxins into the water. Other compounds, such as H2S, and metals may also become more soluble and affect water quality.
Given the importance of the thermocline, an automated intelligent measurement/monitoring approach is useful to identify, characterize, and monitor the thermocline both spatially and temporally.